Lamp base



FIG. 1 is a side view of the lamp base, with all sides being the same;

FIG. 2 is a top view thereof, with the unclaimed cap partially removed in order to allow the shape of the top to be seen; and,

FIG. 3 is a bottom view thereof.

The broken lines represent environment of use and form no part of the claim. 

The ornamental design for a lamp base, as shown and described. 